1. Field of the Invention
The present invention relates to methods and apparatus for producing valuable minerals from the earth. More particularly, the invention relates to an apparatus and method for setting pipe anchors to secure the position of downhole well tools such as annulus packers and subsequently releasing the tool for removal from the well.
2. Description of Related Art
Downhole well tools most commonly used to secure pipe or another tool such as an annulus packer to the inside wall of a wellbore casing are frequently characterized as xe2x80x9cslipsxe2x80x9d. Characteristically, a slip comprises a plurality of radially expansible elements known to the art as a xe2x80x9cwickers.xe2x80x9d Traditionally, a plurality of wickers are distributed circumferentially around a cylindrical mandrel. By some means, the wickers are longitudinally secured to the mandrel, but radially free to at least limited expansion from the mandrel outside diameter. The inside wall engagement surfaces of a wicker are serrated with numerous penetrating tooth points or parallel rows of cutting edges. The wicker teeth or edges are of extremely hard material and are cut sharply for penetration into the steel casing wall surface. The wicker underside is ramped to cooperate with a conical slip face. The conical slip face is a circumferential surface on a tubular sleeve. By one of various means, the tubular sleeve is displaced axially along the mandrel surface relative to the longitudinally fixed wicker to wedge the conical slip face under the wicker and against the underside ramp. As the conical slip face advances axially along the mandrel, the wicker body is forced radially outward to press the serrated tooth edges into the inside wall of the casing thereby clamping the wickers and mandrel to the casing, for example. The mandrel is frequently secured to a tubular workstring such as production tubing or drill pipe but may also be wireline deployed.
Slips used in conjunction with annulus packers are frequently arranged in pairs. One or more slip sets are above the packer and one or more are below the packer. Distinctively, the wickers of the respective slips are biased in opposite directions. For example, the bottom wickers may be biased to cut more deeply into the casing wall if uploaded. Cooperatively, the upper slips may be biased to cut more deeply into the casing wall if downloaded. Hence, longitudinal movement of the packer along the casing bore, for example, is resisted in both directions. However, utility of this nature requires that the several tools be deployed sequentially. For example, a packer unit may comprise four distinct tools: (1) a debris barrier, (2) an upper slip set, (3) a lower slip set, and (4) a packer sleeve. When the packer unit is located at the desired setting position, a predetermined deployment sequence may require that the debris barrier is first deployed. Next, the procedure may specify engagement of the upper slip set to anchor the unit to the casing wall in support of the workstring weight. Third, the packer sleeve is inflated/expanded radially outward to pressure seal the annulus between the inside casing wall and the outer tool string wall. Finally, the lower slip is set to oppose any possible downhole pressure lifting of the work or production string.
Should, by error or accident, either or both slips be set prematurely, the location of the packer may be incorrect or the integrity of the packer seal may be compromised. To mechanically order the deployment sequence of slips and other well tools, mechanisms such a shear pins, shear rings, keys and J-slots have been used with limited success. However, these devices require that a channel of one form or another be cut into the tool mandrel to such depth as to encroach upon the ultimate tool strength. For example, a shear ring groove turned into the tubular wall of a slip mandrel may reduce the cross-sectional diameter by as much as 0.200 in. When translated to the loss of mandrel tensile strength, this 0.200 in. is significant.
In some cases, it is necessary to recover the tools set by a multiple step sequence. In those cases, recovery requires that the sequence be substantially repeated in the same order as that required by the setting.
An object of the present invention, therefore, is a slip setting system that may be sequenced into and out of well or pipe wall engagement.
Another object of the invention is a slip system that may be selectively programmed for the order of tool engagement and disengagement.
Also an object of the invention is provision of collet fingers on a slip actuating cone to prevent the slip from prematurely setting.
Another object of the invention is a mechanical connection between collet fingers from a slip cone and a slip cage that allows the cone and cage to move together during retrieval but to separate against a calibrated shear fastener when set.
A further object of the invention is provision of a retreivable packer system.
An additional object of the invention is a method and apparatus for releasing a downhole pipe anchor.
A further object of the invention is a method and apparatus for rectifying movement of a packer slip element along the packer mandrel.
These and other objects of the invention as will become evident from the following description of the preferred invention embodiments are served and accomplished by a well wall anchor having a reversible deployment mechanism. The well anchor comprises a tubular wicker shoe cage having a sliding fit over a tubular tool mandrel. The shoe cage has plurality of shoe retaining slots around the cage circumference for retaining a plurality of wicker shoes. A conical slip face is carried by an anchor actuating sleeve having collet fingers projecting axially from the slip face. The collet fingers are secured to the cage by calibrated shear pins that fail within a relatively narrow but predetermined load range. The anchor wicker shoes include retainer blocks that mesh with the shoe retaining lots in the shoe cage. An inside surface of the wicker shoes, opposite from the wicker teeth, is ramped to serve as a slip face. The wicker shoe slip face is aligned in juxtaposition with the conical slip face. The shear pins fail upon sufficient axial compression between the collet sleeve and the wicker shoe cage. The wicker expansion cone may advance against the wicker ramps to expand the wicker shoes radially for engagement of the wicker teeth with the well casing wall.
The combination packer and anchor is assembled over a tubular mandrel having two fixed reference structures. The upper reference structure is the mounting collar for a debris barrier. The second reference structure is a ring piston that is structurally secured to the mandrel. The radially expansible elements comprising a debris barrier, the packer sealing sleeve and upper and lower slip anchors are operatively slidable over the mandrel between the two reference structures.
The ring piston cooperates with a double acting cylinder to axially compress the radially expandable elements of the packer. Well string bore pressure applied through a mandrel orifice into a cylinder having the ring piston as one head and a mandrel slide ring as the other head drives the cylinder against the expandable packer elements. The expandable elements are consequently compressed against the upper reference structure and expanded. These elements expand sequentially in a predetermined order as determined by calibrated shear fasteners and the relative dimensions of axial shift channels. First, the debris barrier expands to shield the lower tools from additional debris interference. Next, the upper anchor is expanded when the calibrated shear fastener between the wicker shoe cage and the actuating sleeve fails. As the wicker shoes expand and the wicker points penetrate the well wall, the compressive load along the mandrel is transferred to the well wall. Subsequently, the expandable seal sleeves of the packer are extended against the well walls. Finally, the calibrated shear fastener between the wicker shoe cage and the actuating sleeve for the lower anchor fails resulting in the lower anchor set.
For collapse of the expandable elements and removal of the packer from the well, the mandrel is cut by any of well known means. Initially, following the cut of the mandrel, tension is drawn on the workstring from the surface to the effect of sliding the uphole portion of the cut mandrel under the anchors and packer. However, the anchor collar of the debris barrier is secured to the mandrel surface and does not slide. Hence, the upper end of the debris barrier sleeve is retracted from the well wall as the anchor collar is displaced axially from the downhole compression collar.
At the location where the debris barrier sleeve is completely retracted, the compression collar engages and abutment surface of the limit ring that is secured to the mandrel. The compression collar is rigidly secured to the upper caging ring and therefore draws the caging ring with it. In turn, limit walls on the wicker shoe retaining slots engage the wicker shoe blocks. Further uphole movement of the mandrel draws the uphole wicker shoes off the conical slip face thereby permitting the shoes to withdraw from engagement with the well wall.
The caging ring also engages the retaining blocks on the collet fingers to pull the collet sleeve and attached compression cup away from the packer seal assembly thereby decompressing the packer seal.
Further uphole displacement of the mandrel brings a section of buttress threads on the mandrel surface into engagement with meshing buttress threads on the collet cone sleeve for the lower anchor. Such meshing provides a positive engagement pick-up on the sleeve thereby pulling the conical slip face away from the lower wicker shoe slip face. Hence, the lower anchor disengages from the well wall. The packer and anchor assembly may now be removed from the well or repositioned to a different depth.